EP4306281A1

EP4306281A1 - Method for the improved cutting of panels and working center that implements such method

Info

Publication number: EP4306281A1
Application number: EP23184430.9A
Authority: EP
Inventors: Giuseppe Martelli; Marco Cecchi; Davide Amadori
Original assignee: SCM Group SpA
Current assignee: SCM Group SpA
Priority date: 2022-07-14
Filing date: 2023-07-10
Publication date: 2024-01-17
Also published as: IT202200014830A1

Abstract

The present invention relates to a method for cutting a panel (P), such as a panel made of wood, plastic, fiberglass and the like, wherein said panel (P) is arranged on a plane wherein said panel (P) has to be cut into a plurality of pieces (Ri), and wherein for each piece (Ri) to be cut by means of a cutting tool, such as a cutter and similar, said method comprises the step of: B. determining the starting point of a cutting path of each piece (Ri), so as to maximize the holding of said piece (Ri) during its cutting.

The present invention also relates to a working center (1) configured to carry out the method for cutting a panel (P).

Description

The present invention relates to a method for the improved cutting of panels and working center implementing such a method.

Field of invention

More specifically, the invention relates to an improved method of cutting wood, fiberglass, plastic, and similar panels, in particular for the so-called nesting, which allows keeping in position even small parts to be cut out in the actual cutting steps and which can be used in any other case where it is necessary to keep in position parts of a wooden panel, or of the other materials mentioned above, of reduced dimensions compared to the panel itself.
In the following, the description will be directed to the nesting-type cutting of wooden panels, but it is clear that the same should not be considered limited to this specific use.

Prior art

As is well known, currently there are, in the machine tool sector, machining centers for carrying out machining on panels such as to allow parts of different sizes and shapes to be obtained from a panel. These obtained parts are used above all in the fields of furniture making, interior fittings, and the like.
In literal terms "nesting" would mean nesting. Generally in the sector at issue the possibility of obtaining parts of panels with particular shapes is meant, to maximize the panel's yield, or minimize the possible waste.
In general, panel working machines have a base, a support surface for at least one panel, arranged on the base, a movable bridge along the base, generally positioned above the surface, and a multifunction machining unit, which equips at least one machining tool for machining the panel.
The panel to be worked rests on a sacrificial panel and is held in position by means capable of creating vacuum. The panel to be machined is placed on top of the sacrificial panel, which in its turn is placed on top of the means for making the vacuum. By transpiration through the sacrificial panel, the panel to be worked is held in place.
Usually, the working tool is a cutter, such as an endmill, suitable for drilling and cutting out the required panel parts. The endmill is moved and driven following a cutting pattern as mentioned to maximize the use of the panel, reducing the waste to a minimum.
The cutting patterns are generally calculated and obtained using suitable and known so-called optimization software.
The effective cut, once the panel is placed on the working surface, is carried out according to a cutting sequence determined by the computer.
The machining tool, i.e., the end mill, is a rotating tool, which rotates at high speed. The high rotation speed of the end mill stresses the part of the panel to be cut out. A technical problem in the industry is the fact that if the part to be cut out is small, the force that holds this part to be cut out, i.e., the vacuum effect on the piece through the sacrificial panel, is reduced.
Therefore, the stress of the working tool (the end mill) could cause the piece's displacement to be cut out itself, and therefore an incorrect cut of the same.
In case of one or more pieces were moved, the correct cutting of the subsequent pieces could also be compromised and therefore the effective performance of the panel.
It is clear that this procedure is onerous in economic and production process terms.

Scope of the invention

In light of the above, it is, therefore, an object of the present invention proposing a method or cutting sequences, which allow keeping the pieces to be obtained from a panel in the predetermined position during the cutting or milling operations.
Another object of the invention is to allow the realization of the optimized cuts obtained from different optimization software.

Object of the invention

It is, therefore, specific object of the present invention a method for cutting a panel, such as a panel made of wood, plastic, fiberglass and the like, wherein said panel is arranged on a plane wherein said panel has to be cut into a plurality of pieces, and wherein for each piece to be cut by means of a cutting tool, such as a cutter and similar, said method comprises the step of: B. determining the starting point of a cutting path of each piece, so as to maximize the holding of said piece during its cutting.
Always according to the invention, said step B may comprise, for each piece to be cut out, the following sub-steps: B1. determining a starting point of the cut; B2. defining the material surrounding ranges; and B3. selecting the starting side of the cut.
Still according to the invention, in said step B1 the initial cutting point may be the central point of one side of the piece.
Advantageously according to the invention, said step B2 may comprise the step of determining, for each side of the workpiece to be cut out, the already cut parts, which are at a predefined maximum distance Distance_Max.
Further according to the invention, said maximum distance Distance_Max may be calculated according to the following equation: ${Distance}_{Max} = 2 \times Cutting Diameter$
wherein Cutting Diameter is the diameter of said cutting tool.
Always according to the invention, said step B3 may comprise the following sub-steps: performing a comparison cycle, starting from one side of the piece, with all the other sides of the same piece, starting from the contiguous one, determining whether the next side can be selected as a starting point with respect to the previous side, wherein if said next side is selected and taken as a reference, a subsequent comparison cycle is performed until the end of the comparisons starting from said selected side;
wherein the selection of one side is made sequentially according to:

the type of element, such that in the comparison between linear and arched sections, the linear section is chosen;
if a side is not determined by the type, then the distribution of the material on the side is considered, such that two sides are selected on the basis of one or more selected selection parameters; and
if a side is not determined by distribution, then the position of the side of the piece is considered, wherein the side is selected according to how the parts (R_i) are cut, selecting the side that guarantees the position based on the sequence of subsequent cuts.

Still according to the invention, obtaining said selected selection parameters may comprise the following steps: calculating the total linear length of the residual material on each side of a piece; calculating the area of the residual material on the side: area of the rectangles of the material that have a thickness other than 0, or that have cut portions; calculating the average thickness of residual material on each side by means of the weighted average of the thickness of the material between the portion of the uncut side, and the distance to the corresponding cut piece; and calculating the defined material coverage on each side as a percentage of the available material.
It is further object of the present invention a working center comprising a working surface, for supporting a panel to be cut into a plurality of pieces according to a cutting scheme, wherein said working surface comprises vacuum means for holding said panel in position, a bridge, movable along said working surface, having a crosspiece, a working unit, arranged movably on said bridge, having at least one working tool, such as a cutter and the like, to cut out said pieces of said panel (P) according to said cutting scheme, and a logic control unit, configured to move said bridge and said working unit to perform said cutting pattern by means of said working tool, wherein said working center is characterized in that said logic control unit is configured to move said bridge and said working unit according to the cutting method as defined above.
It is also object of the present invention a computer program comprising instructions which, when the program is executed by a computer, causes the computer to execute the steps of the method as defined above.
It is finally object of the present invention a computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to execute the method as defined above.

Brief description of the figures

The present invention will be now described, for illustrative but not limitative purposes, according to its preferred embodiments, with particular reference to the figures of the enclosed drawings, wherein:

figure 1 shows a first perspective view of a working center for carrying out a nesting-type machining;
figure 2 shows a second perspective view of the working center according to figure 1;
figure 3 shows a panel showing the pieces to be obtained by milling, as determined by an optimization software;
figure 4 shows a panel to be divided into parts, in which guidelines are shown which indicate the cutting path;
figure 5 shows a scheme for calculating the grip factor of a piece;
figure 6 shows a first example of a starting point for cutting pieces of a panel;
figure 7 shows a second example of a starting point for cutting pieces of a panel;
figure 8 shows an exemplary cutting scheme for determining an optimized cutting sequence;
figure 9 shows the cutting diagram of figure 8, in which a calculation grid is shown;
figure 10 shows an exemplary cutting pattern for determining the starting piece for cutting;
figure 11 shows a further exemplary cutting pattern for determining the starting piece for cutting;
figure 12 shows a cutting diagram in which the intervals of material with respect to a piece of interest to be cut are determined;
figure 13 shows determining material coverage of one side of a workpiece to be cut;
figure 14 shows a first cutting pattern with gaps of material coupled to the piece to be cut;
figure 15 shows a second cutting pattern with gaps of material coupled to the piece to be cut;
figure 16 shows a side view of a cutting path of a machining tool;
figure 17 shows a top view of the cutting path of figure 16;
figure 18 shows a section of the uncut part of the piece to be cut following the cutting of the initial side; And
figure 19 shows the cutting perimeter of the piece to be cut out.

Detailed description

In the various figures, similar parts will be indicated with the same reference numbers.
With reference to figures 1 and 2, a working center 1 can be seen configured for carrying out nesting-type operations.
In particular, the working center 1 comprises a base 11, a working surface 12, on which the panel P to be cut or worked in general can be arranged, a bridge 13, movable along the base 11, so as to overlap the surface working surface 12, on which the panel P to be machined can be arranged, and a protecting cabin 14, arranged around the bridge 13.
The working surface 12 comprises means for the vacuum (not shown in the figures), on which a sacrificial panel can be arranged, suitable for allowing the transpiration of the vacuum, to keep the panel to be worked P in position.
The protecting cabin 14 has the main purpose of preventing chips or machining scraps, caused by the high-speed rotation of the machining tools, from hitting a user. The protecting cabin 14 also has a window 141, to allow visual control of the machining.
The bridge 13 comprises a cross member 131 and guide means 132.
Furthermore, the machining center 1 also comprises a working unit 15, arranged movably on said bridge 13, and in particular coupled slidingly to the guide means 132, so as to be movable along a direction transverse to that of development of the base 11.
Once the panel P to be machined is arranged on the working surface 12, i.e. on the sacrificial panel (not shown in the figure), movement along the X and Y axes of the bridge 13 and of the working unit 15 allows, for example, the cutter (not shown in the figures) installed on the working unit 15, to cut out the parts from the panel P according to a logical cut, calculated by a computer program of known type, by means of a logic control unit 16, which also performs a computer program based on an improved panel cutting method as described below.
With reference now to figure 3, a cutting scheme or nesting scheme of a panel P can be observed. As can be seen, the panel P is divided into a plurality of pieces R_i, having different shapes, some even irregular.
The panel P is arranged with respect to a reference of the working surface 12, called the nesting angle O. Basically, said nesting angle O is nothing more than a pre-set abutment point for the panel P to be machined, which is also used as a reference system. The nesting angle O is the point where the vacuum grip is greatest.
Furthermore, the points of the plane can be referred to with respect to a Cartesian plane according to the axes indicated with X and Y, which are arranged precisely in correspondence with the sides of the plane. In this case, the nesting angle O coincides with the origin of the Cartesian plane. In other embodiments, other reference systems may be used.
By means of the aforementioned reference system, the machining unit, which the working center is equipped with, together with the data relating to the logical cut of the panel P, can report and dispose of the position on the working surface 12 of the panel P and, therefore, of the various parts R_i to cut out.
To maximize the hold of the various pieces R_i when they are cut out from panel P, three main procedures or steps are mainly used, namely a procedure for defining the cutting sequence by proximity, a procedure for defining the automatic starting or initial point, and a procedure for defining the progressive cutting strategy. Each of the above procedures is described below.

Definition of the cutting sequence by proximity

With reference to figure 4, a first simple example of the proximity cutting algorithm is shown, in order to generally understand the algorithmic logic of this procedure.
With a cutting pattern or pattern very regular like the one shown in said figure 4, it is started from the piece numbered R₁, in correspondence to the point opposite to the nesting origin O, which is the point, as mentioned, where the vacuum grip is generally less, the external edges are followed, indistinctly proceeding horizontally or vertically, until arriving at the final piece R₁₂ placed at the origin or at the nesting angle.
In other words, the progressive numbering of the pieces R_i is followed, i.e., R₁, R₂, R₃,..., R₁₂. In other words, the series of pieces in the vertical direction is executed first R₁, R₂, R₃, in order to cut out or obtain the pieces R_i further away from the nesting angle O.
Subsequently, maintaining the same rule of cutting out the pieces R_i further away from the nesting angle O, which have a smaller vacuum grip, but which at the same time have a greater number of sides or a portion of the perimeter coupled to other adjacent pieces.
In this connection, the obtaining in sequence of R₁₀, R₁₁, and R₁₂ after R₃ would be excluded because it would be leaving six pieces R_i isolated and with a lower overall coupling to the working surface 12.
Therefore, the initial piece R₁ starting point is such because it has a position of less grip, which is however compensated, as mentioned, by having more material (of panel P) around it. As it is progressed, the pieces R_i during the cutting steps will have on average less and less material around (or around) to keep them in position, but they will also be in positions of ever greater depression. This is basically the logic followed to maximize the minimum depression of a cutting sequence.
A difficulty in applying the indicated logic consists in determining the pieces to be cut along the directions, as the cutting patterns can also be very irregular in shape.
The design of the cutting sequence algorithm involves, in general terms, the following sub-problems, the solution of which is briefly described below:

determination of gripping factor (grip factor);
determination of the piece R_i starting point for each cutting line;
determination of pieces R_i to be sequenced along the two directions, horizontal and vertical; and
choose the cutting line using a criterion.

These sub-problems must be solved individually to be able to determine an overall solution.
As regards the determination of the grip factor (or grip factor), it is a matter of determining a metric capable of detecting the degree of grip at the moment in which the piece R_i is stressed in the effective cutting step by the tool as it rotates. The grip factor is here encoded as a decimal number in the range [0, 1 ], where 0 corresponds to a minimum grip, and 1 to a maximum grip. Of course, other forms of coding may be provided in other embodiments.
In the example shown in figure 4, if the piece R₈ is cut first, this would have a grip factor equal to 1 since the entire perimeter, i.e. all four sides, are still uncut and coupled to the surrounding pieces; instead, if the piece R₁ is cut first, its grip factor would be a number close to 0.75, being surrounded on three sides by solid, i.e. by other pieces R_i surrounding.
Obviously, the pieces R_i can have free or irregular shapes. The grip factor algorithm proceeds by calculating an offset curve of a part, where the amount of offset is a parameter.
More specifically, referring to piece R₂₀ of figure 5, the offset curve is an increased perimeter of said piece R₂₀ to be cut R_i, indicated with the line Lo.
Between the line Lo and the effective boundary line of piece R₂₀, an offset area is underlying, denoted by Ao. Part of the offset area Ao is superimposed on the already cut neighboring piece, which in the case at issue is R₁₉.
The grip factor is calculated as the ratio of the offset area Ao relative to the uncut perimeter portion, i.e. superimposed on the uncut pieces and therefore still coupled to the reference piece (i.e. R₂₀ in the example shown), and the offset data area Ao overall. In the present case, since the pieces have small dimensions, a uniform area coupling is considered. In other embodiments, the coupling force can be modeled by a suitable function.
Therefore, in the part of the plane included between said offset curve Lo and the profile curve of the piece R_i, the areas made up of the empty parts, which have already been cut, are counted, to return the ratio between the sum of these areas and the offset total area Ao.
For performance reasons, panel P is discretized and the calculation of the areas is reduced to the sum of points of the resulting grid.
As regards the determination of the piece R_i point of departure for each cutting line (vertical or horizontal), it must be considered that the ideal starting point does not always have a corresponding piece R_i. In some even worse cases, piece R_i at the sweet spot is not the best piece for starting.
The starting point for the cut is by definition the one furthest away from or opposite the nesting angle O.
However, even a simple case like the example in figure 4, the first type of drawback occurs, as shown in figure 6. In this case, we have that in the starting point there is no piece R_i to cut.
A case that presents the second type of drawback (starting point not at piece R_i best, at least by far) is the one shown in figure 7. In this case, we have that piece R_i at the ideal starting point is piece R₁, precisely because it is opposite to the nesting angle. However, if it is started from piece R₃ horizontally to obtain the pieces R₃, R₄, or it is desired to cut piece R₁₃ before piece R₁, there would not be a worse situation than starting from piece R₁. Therefore, there would be a "decisional" ambiguity in the algorithm.
For determining the starting piece R_i, the distance in a straight line from the origin of the is taken into account nesting and the distance in x (y) if the cutting line is along Y (X), to combine these two values in a count that chooses piece R_i with a lower score.
In other words, having the cutting line, which can be parallel to the X or Y axis, for the choice of piece R_i to be cut first, the distance D_Ri is considered (X, Y) of each (discrete) point of each piece R_i to be cut of the logical cut from the point opposite to the point of the panel P furthest from the nesting corner O, indicated with D_Ri (x, y), and the distance of each of said points from the axis of the X or Y cutting line, indicated by D_Ri-X (x, y) o D_Ri-_Y (x, y). The ratio between these distances is then calculated, which is defined as Score, calculated for the case in which the X direction is $ScorIt {is}_{X} = \frac{D_{RiX} (x, y)}{D_{Ri} (x, y)}$
piece R_i the starting point is the one that has the point with the lowest score.
Regarding the determination of pieces R_i to be sequenced along the two horizontal and vertical directions, i.e., parallel to X and Y, in the first example shown in figure 4, it is immediate to establish the sequence of horizontal or vertical pieces starting from a given piece, simply on the basis of the criterion for which it is necessary to start from the farthest point from the nesting angle O.
Considering a more complex case, such as the one shown in figure 8, it is supposed to start from the position indicated in the figure with "START", therefore from the piece numbered R₈, which as it can be seen has, among other things, an irregular shape.
Considering figure 9, it can be observed that the vertical cutting line (parallel to the Y axis, as shown in figure 9 itself) includes, in the case shown, several pieces R_i aligned on the same Y axis.
More specifically, the part of the plane included between the vertical lines at the ends of piece 8 is considered, as projected onto the X axis, perpendicular to the Y axis, thus proceeding downwards. It is then considered the different measures of ordinate y, i.e. y₁, y₂, and y₃ (still referring to figure 9) that meet the various pieces R_i, there is not one and only piece R_i intersected with the corresponding horizontal line.
As can be seen, along y₁ pieces R₇ and R₁₅ meet, along y₂ pieces R₂ and R₆ meet, and along y₃ pieces R₁₁, R₁₁, R₁₀, R₉ and R₅ meet.
The piece R_i chosen, therefore, is the one most external with respect to the origin of the nesting O, therefore, once the cutting line has been determined (Y in the example at issue), the one further and further away. In this way, a certain convexity of the part of the panel P will be maintained as much as possible, which remains after each cut, without leaving "holes", i.e. pieces R_i with a low grip factor or below a certain predefinable threshold.
There is the step of proceeding along the Y (X) cutting line between two pieces aligned with a certain tolerance (which is a given parameter) in X (Y), choosing the piece R_i outermost in X (Y) with respect to the nesting origin O.
In the example shown in figure 9, by applying the step described above, the sequence corresponding to the Y cutting line starting from piece R₈ would be: R₈, R₇, R₆, R₁₀, R₅.
However, the cutting sequence as indicated presents a further problem and, in this sense, the example shown in figures 8 and 9 is not accidental. When it comes to cutting piece R₁₂, in fact, the grip factor would be reduced due to having already cut piece R₁₀. In other words, with this sequence, it is had that piece R₁₂ would be too weakened, presenting a grip factor below a predefined threshold. It is considered that if piece R₁₂ is cut first, then piece R₁₀, and finally the piece R₅, the minimum grip factor of the sequence would be greater than the other sequence.
This is basically because the piece R₁₀ constitutes a "plug", as mentioned, between piece R₁₂ and piece R₆, i.e. it would weaken the next piece to be cut in the sequence. In order not to create fragmentation, a plug needs all the previous pieces it subtends to be executed, so that it can continue along the cutting direction (cutting line).
The algorithmic step indicated above is therefore specified in some embodiments considering that when proceeding along a cutting line, a "plug" is identified, the sequence must be terminated at the immediately preceding piece R_i, naturally on the basis of a predefined minimum grip factor threshold.
It is now considered the step of choosing the cutting line. When it is necessary to make a choice of the cutting line, generally parallel to one of the reference axes X or Y in the present embodiment of the method for the improved cutting of panels P. Therefore, criteria are adopted which are evaluated in a specific order.
The choice of the direction takes place by evaluating and following the one that creates fewer "holes", or, as defined above, fewer pieces still to be cut in a back position with respect to the forward direction, as in the case shown in figures 10 and 11, which does not represent an optimal sequence, as, for example, cutting piece R₄ before the pieces from R₈ to R₂ would leave a substantial hole, formed by the part of the panel between the pieces R₁, R₃, and R₄, which would be greatly weakened. In other words, by cutting R₄ the portion of panel P given by the pieces R₈, R₇, R₆, R₅ and R₂ would be left weakened, as the various pieces would have a lower average grip factor value.
So if this were the result of the horizontal sequence, it would be preferable to choose the vertical sequence R₁, R₂.
In particular, the minimum grip factor of the longitudinal direction (Y) is calculated having first cut the transversal one (X) and vice versa. Of the two directions, the sequence that provides the highest overall minimum grip factor is chosen first.
In complicated situations where pieces R_i are very "immersed" or nested one in the other, cutting a sequence inevitably affects the creation of "holes" for the next one, and, to understand which of the two to cut first, it would be necessary to "simulate" all possible future choices up to the end of the machining or at least until reaching the same machining status before the end (unlikely event).
The above entails a considerable computational load, which is often not negligible due to the processing times required. For this, an approach is adopted, which is based on the fact that the sequence initially identified and then not chosen will not change significantly, therefore, it is possible to carry out a rather independent a priori evaluation of the grip factor.
Finally, the overall deviation in X (Y) for transverse (longitudinal) sequences between the centers of gravity of the pieces in the given sequence is calculated.
Finally, this distance is normalized with respect to the number of pieces R_i of the sequence, choosing the sequence with minimum distance.
Therefore, it is followed the principle that the shorter the distance, the more aligned the pieces will tend to be, the ideal being the situation where the pieces R_i are perfectly aligned, as in the case of figure 4, where the pieces R_i to be cut are all aligned.
Based on the above, the following main steps and sub-steps of the proximity cutting procedure as described above can be summarized:

identification of starting points;
- ∘ identify the starting point for the longitudinal sequence (Y direction);
- ∘ identify the starting point for the transversal sequence (X direction);
determination of ordered sequences;
- ∘ calculating the ordered sequence for the longitudinal sequence with the starting piece found in step A;
- ∘ calculating the ordered sequence for the transversal sequence (X) with piece R_i starting point found in step A;
choice of cutting line;
- ∘ calculation of the metric for the two indicated sequences, longitudinal (Y) and transversal (X);
- ∘ if the difference between the two metrics is lower than a certain threshold, proceed, otherwise choose the sequence with the best metric and go back to step A;
- ∘ calculating the metric for the two sequences;
- ∘ if the difference between the two is lower than a certain threshold, proceed, otherwise choose the sequence with the best metric and go back to point A;
calculating the grip factor metric in the direction of the two sequences;
- ∘ if the difference between the two is lower than a certain threshold, proceed, otherwise choose the sequence with the best metric (grip factor) and go back to point A;
- ∘ fork and proceed by examining both sequences, without favoring one. At the end of this step, by virtue of the possible bifurcations that can occur when the partial solutions are comparable, a list or file of solutions will be obtained.

The final step is to evaluate the best solution.
The score used is that of the minimum sum of the grip factors of the individual pieces R_i calculated following the order given by the sequence.
The algorithm at issue is, broadly speaking, a "pattern matching" algorithm, as can be seen.

Definition of the automatic starting point+

The strategy for calculating the automatic starting point of the cutting sequence has as its objective the choice of a starting point of cut that maximizes the amount of material held for each piece R_i during the respective cut.
Preliminarily, there is the definition step of the material ranges of each specific piece R_i. In particular, the optimization of the initial position of the piece R_i cut provides as a preliminary step the construction of the intervals of material available on each side of the piece R_i chain.
Usually, it is not started from the edge of piece R_i to be cut, also for stability reasons. It is tried to choose a starting point on the perimeter of the specific piece R_i, which allows keeping piece R_i anchored as much as possible to a part of the uncut panel P.
Referring to figure 12, with respect to the geometric profile of the piece R_i object of analysis, for each relative side the perimeter parts already cut are determined which are at a maximum predefined distance equal to ${Distance}_{Max} = 2 \times CutingDiameter$
in which Cutting Diameter is the diameter of the tool (typically, for example, a cutter) used to cut the part, thus the distance of the cut material around the profile of the part.
For each of these, a rectangle of material is constructed (indicated with a slightly wavy line), which identifies the linear overlap along the side and the residual thickness of material between the 2 parts. If one side does not intercept any part already cut, entirely or partially, the gap of material has thickness equal to that of the CutDiameter. In case the side overlaps one side of the sheet, the material thickness is set to 0.
In other words, for each side of piece R_i to be cut out for analysis, the already cut neighboring pieces are considered, the overlapping is projected onto the closest side, the aforementioned wavy rectangle is obtained, which represents the overlapping portion.
Then there is the evaluation of the best starting side. Once the material gaps on each side of the part profile R_i have been calculated to analyze or to cut, it is moved on to the evaluation of the best side. By definition, the initial starting point is placed in the middle of a side and the distance is determined by the rotation of the tool. Generally the cutting direction is in agreement with the rotation direction of the tool, e.g., an endmill.
For each side it is calculated (with reference to figures 12, 13, 14, and 15):

the total linear length of the residual material on the side: this is the sum of the lengths of the rectangles of material that have a thickness other than 0;
the area of the residual material on the side: area of the rectangles of material that have a thickness other than 0;
average thickness of residual material on the side: weighted average of the thickness of the rectangles of material; and
material coverage: the percentage coverage of the material is defined on the side, with a scale that has 100% at the midpoint of the side and 0% at the initial point (see in particular figure 13).

These analyses make it possible to understand whether or not there is material available near the starting point of the cut and consequently whether the section, when it is performed at the end of the cut, will have material all the way through or not.
The same type of calculation of the material on the side is done by imagining that the current side is the last side to be cut (optimum side hypothesis; see figures 14 and 15).
Basically, the same calculations are carried out backwards, from the first element of the profile to the element under analysis according to the distance defined by the rotation of the tool.
This information allows detecting if the current side will be the last to be cut and how much material it will have available during the cut.
The selection step of the side of the piece R_i is then carried out to cut out.
In particular, once the material on each side of the piece to be cut has been evaluated, each side is checked against each of the others until the best one is identified.
In essence, a comparison cycle is performed starting from the i-th side with all the other sides starting from the (i+1)-th (contiguous to the i-th side), up to the end, if the (i+1)-th side is better, it is taken as a reference, and the cycle starts again until the end of the comparisons.
The selection is made sequentially according to the following criteria:

1. type of element: in the comparison between the linear and arched section, the linear section is always taken, to avoid starting the cut on a curved section;
2. better distribution of the material on the side: the best side of the two under analysis is chosen based on the parameters calculated previously;
3. best side position: the best side is chosen according to how the R_i parts will be cut, looking for the side that guarantees the best position keeping in mind how the cutting sequence definition algorithm works.

Regarding the advance from the vertex opposite to the reference one, the criteria are executed sequentially starting from criterion 1, if the best side is found the algorithm terminates, otherwise it passes to criterion 2, if the best side is found the algorithm terminates, otherwise it passes to criterion 3, which finally identifies the side.

Definition of the progressive cutting strategy

The cutting strategy of the nesting small parts R_i has the objective of maximizing the uncut material during the actual cutting step, in order to keep as much material as possible in common with the uncut sheet or part of panel P.
Generally, for example considering an endmill, the cut is performed in a single pass along the profile of the part with a progressive in depth in the first section to increase the material in contact.
The procedure essentially consists of the following steps, which can be better understood by referring to figures 16 and 17, which show piece R_i to be cut respectively in a side and top view:

a vertical entry is made into the panel material P at the entry point at a non-through depth (entry depth d₁). In the figure, S denotes the sections of the path followed by the tool, e.g. an end mill. As can be seen, initially the tool carries out the section S₁, penetrating for an inlet depth indicated by d₁ in the piece to be cut out R_i, which is naturally smaller than the piece thickness R_i to cut out;
an advancement is carried out with a sort of linear ramp to greater depth up to a point that precedes the end of the section or cut (i.e., a distance for final depth application), as shown in figure 16. In this case, therefore, it is followed the section of the path S₂, reaching the end of the panel by depth, but not at the vertex, but before it for a finishing distance d₂, to avoid chipping the panel on the edge.

In the two sections S₁ and S₂, the path of the machining tool is not contained in a plane perpendicular to the part to be cut out R_i. In said first section S₁ the tool moves laterally away from the piece R_i itself that is cutting, while in the second section S₂ the tool approaches the piece R_i, getting closer to the piece R_i itself.
With reference to figure 1, a section of piece R_i can be observed along the first side to be cut, after the tool has made the cuts along the sections S₁ and S₂. In particular, it is possible to observe, still in section, the surface of the material, which remains uncut.
In a preferred embodiment, this offset (the paths S₁ and S₂) can be moved laterally at the entry point with respect to the actual section point, to avoid the risk of chipping the panel P.
In this way, the first cutting side maintains a portion of unmachined material, which the shape shown in side view, as mentioned, schematically in figure 18, to allow a greater sealing area of the piece P.
Also referring to figure 19, the machining will advance for all the remaining profiles with a passing depth, and in the last section, i.e. the last side, it will complete the cut, working the intact semi-side (see figure 18) and the pre-machined semi-side, so as to properly finish the obtained part.

Advantages

An advantage of the cutting method according to the present invention is that it allows maximizing the grip of even small-sized pieces on the machine table, obtaining more precise sequential cuts.
A further advantage of the present invention is the fact that the cutting method can be easily implemented in a computer.
Another advantage of the present invention is that of allowing the installation of said cutting method in working centers not equipped with the same, such as to allow the possibility of upgrading them by using software.
The present invention has been described for illustrative but not limitative purposes, according to its preferred embodiments, but it is to be understood that modifications and/or changes can be introduced by those skilled in the art without departing from the relevant scope as defined in the enclosed claims.

Claims

Method for cutting a panel (P), such as a panel made of wood, plastic, fiberglass and the like, wherein said panel (P) is arranged on a plane wherein said panel (P) has to be cut into a plurality of pieces (R_i), and wherein for each piece (R_i) to be cut by means of a cutting tool, such as a cutter and similar, said method comprises the step of:
B. determining the starting point of a cutting path of each piece (R_i), so as to maximize the holding of said piece (R_i) during its cutting.
Method according to the preceding claim, characterized in that said step B comprises, for each piece (R_i) to be cut out, the following sub-steps:
B1. determining a starting point of the cut;

B2. defining the material surrounding ranges; and

B3. selecting the starting side of the cut.
Method according to the preceding claim, characterized in that in said step B1 the initial cutting point is the central point of one side of the piece (Ri).
Method according to any one of claims 2 or 3, characterized in that said step B2 comprises the step of determining, for each side of the workpiece (Ri) to be cut out, the already cut parts, which are at a predefined maximum distance Distance_Max.
Method according to the preceding claim, characterized in that said maximum distance Distance_Max is calculated according to the following equation: ${Distance}_{Max} = 2 \times Cutting Diameter$
wherein Cutting Diameter is the diameter of said cutting tool.
Method according to any one of claims 2-5, characterized in that said step B3 comprises the following sub-steps:
performing a comparison cycle, starting from one side of the piece (R_i), with all the other sides of the same piece (R_i), starting from the contiguous one, determining whether the next side can be selected as a starting point with respect to the previous side, wherein if said next side is selected and taken as a reference, a subsequent comparison cycle is performed until the end of the comparisons starting from said selected side;

wherein the selection of one side is made sequentially according to:
the type of element, such that in the comparison between linear and arched sections, the linear section is chosen;

if a side is not determined by the type, then the distribution of the material on the side is considered, such that two sides are selected on the basis of one or more selected selection parameters; and

if a side is not determined by distribution, then the position of the side of the piece (R_i) is considered, wherein the side is selected according to how the parts (R_i) are cut, selecting the side that guarantees the position based on the sequence of subsequent cuts.
Method according to the preceding claim, characterized in that obtaining said selected selection parameters comprises the following steps:
calculating the total linear length of the residual material on each side of a piece (R_i);

calculating the area of the residual material on the side: area of the rectangles of the material that have a thickness other than 0, or that have cut portions;

calculating the average thickness of residual material on each side by means of the weighted average of the thickness of the material between the portion of the uncut side, and the distance to the corresponding cut piece; and

calculating the defined material coverage on each side as a percentage of the available material.
Working center (1) comprising
a working surface (12), for supporting a panel (P) to be cut into a plurality of pieces (R_i) according to a cutting scheme, wherein said working surface (12) comprises vacuum means for holding said panel (P) in position,

a bridge (13), movable along said working surface (12), having a crosspiece (131),

a working unit (15), arranged movably on said bridge (13), having at least one working tool, such as a cutter and the like, to cut out said pieces (R_i) of said panel (P) according to said cutting scheme, and

a logic control unit (16), configured to move said bridge (13) and said working unit (15) to perform said cutting pattern by means of said working tool,

wherein said working center (1) is characterized in that said logic control unit (16) is configured to move said bridge (13) and said working unit (15) according to the cutting method according to any one of claims 1-7.
A computer program comprising instructions which, when the program is executed by a computer, causes the computer to execute the steps of the method according to any one of claims 1-7.
A computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to execute the method steps according to any one of claims 1-7.